Polyarylene sulfide-containing polymer melt

ABSTRACT

This invention relates to methods for decreasing the complex viscosity of a polyarylene sulfide polymer melt while maintaining the molecular weight of the polyarylene sulfide with time. This invention also relates to polymer melt compositions comprising a polyarylene sulfide, wherein the complex viscosity of the composition is decreased relative to the complex viscosity of the native polyarylene sulfide measured under the same conditions, and the weight average molecular weight of the polyarylene sulfide is maintained. The methods of decreasing the complex viscosity of a polyarylene sulfide-containing polymer melt, and the polymer melt compositions so obtained, are useful in processes to produce fibers, films, nonwovens, and molded parts from polyarylene sulfides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalApplication No. 61/316,053 filed on Mar. 22, 2010, which is hereinincorporated by reference in its entirety.

FIELD

This invention relates to a polyarylene sulfide melt, and the viscosityand molecular weight thereof.

BACKGROUND

Polyphenylene sulfide (PPS) is a commercially-available thermoplasticpolymer that is widely used for film, fiber, injection molding, andcomposite applications due to its high chemical resistance, excellentmechanical properties, and good thermal properties. In the presence ofair and at elevated temperatures, the thermal and thermooxidativestability of PPS is considerably reduced. Typically, PPS is processed inthe melt at about 300° C. or higher, and partial decomposition canoccur, resulting in loss of polymer properties and reduced productivity.

In applications such as the production of fibers, films, nonwovens, andmolded parts from polyarylene sulfide resins such as PPS, it isdesirable that the molecular weight of the polymer resin remainsubstantially unchanged during processing of the polymer. Variousprocedures have been utilized to stabilize polyarylene sulfidecompositions such as polyphenylene sulfide against changes in physicalproperties during polymer processing.

U.S. Pat. No. 4,411,853 discloses that the heat stability of arylenesulfide resins is improved by the addition of an effective stabilizingamount of at least one organotin compound which retards curing andcross-linking of the resin during heating. A number of dialkyltindicarboxylate compounds used as cure retarders and heat stabilizers aredisclosed, as well as di-n-butyltin-S,S′-bis(isooctyl thioacetate) anddi-n-butyltin-S,S′-bis(isooctyl-3-thiopropionate.

U.S. Pat. No. 4,418,029 discloses that the heat stability of arylenesulfide resins is improved by the addition of cure retarders comprisingGroup IIA or Group IIB metal salts of fatty acids represented by thestructure [CH₃(CH₂)_(n)COO-]-₂M, where M is a Group HA or Group IIBmetal and n is an integer from 8 to 18. The effectiveness of zincstearate, magnesium stearate, and calcium stearate is disclosed.

U.S. Pat. No. 4,426,479 relates to a chemically stabilizedpoly-p-phenylene sulfide resin composition and a film made thereof. Thereference discloses that the PPS resin composition should contain atleast one metal component selected from the group consisting of zinc,lead, magnesium, manganese, barium, and tin, in a total amount of from0.05 to 40 wt %. These metal components may be contained in any form.

U.S. Pat. Nos. 3,405,073 and 3,489,702 relate to compositions useful inthe enhancement of the resistance of ethylene sulfide polymers to heatdeterioration. Such polymers are composed of ethylene sulfide unitslinked in a long chain (CH₂CH₂—S)_(n), where n represents the number ofsuch units in the chain, and are thus of the nature of polymericethylene thioethers. The references note that the utility of thesepolymers as plastic materials for industrial applications is seriouslylimited, however, due to their lack of adequate mechanical strength. Thereferences disclose that an organotin compound having organic radicalsattached to tin through oxygen, such as a tin carboxylate, phenolate oralcoholate, is employed to enhance resistance to heat deterioration ofethylene sulfide polymers. The references note that the efficacy of theorganotin compounds is frequently enhanced by a compound of anotherpolyvalent metal, or another tin compound. The second polyvalent metalcan be any metal selected from Groups II to VIII of the Periodic Table.Given the different chemical reactivity and physical properties ofethylene sulfide polymers as compared to polyarylene sulfides, it wouldnot be obvious that the same additives would have the same effect inpolyarylene sulfides as in ethylene sulfide polymers.

In light of the decomposition of polyarylene sulfides which can occur attypical processing temperatures, it is desirable to use a lowerprocessing temperature. Stated another way, it is desirable to decreasethe viscosity of a polymer melt comprising polyarylene sulfide so thatpolymer processing can be performed at lower temperatures where thethermal and thermooxidative stability of the polyarylene sulfide areimproved. Being able to process a lower viscosity polyarylene sulfidemelt also offers the advantage of lower pressure drop during fiberspinning and improved flow during injection molding. Also desired aremethods of reducing polyarylene sulfide melt viscosity while maintainingthe molecular weight of the polyarylene sulfide with time.

SUMMARY

This invention provides methods for decreasing the complex viscosity ofa polymer composition comprising polyarylene sulfide while maintainingthe weight average molecular weight of the polyarylene sulfide. Thepresent invention also provides a polymer melt composition comprising:a) a polyarylene sulfide having certain weight average molecular weightand complex viscosity characteristics, and b) at least one tin additivecomprising a branched tin(II) carboxylate. The complex viscosity of themelt composition is decreased compared to that of the native polyarylenesulfide measured under the same conditions; and the retention of theweight average molecular weight of the polyarylene sulfide in thecomposition is at least about 80% when measured according to theAccelerated Aging Test defined herein.

In one embodiment, this invention provides a polymer melt compositioncomprising (a) a polyarylene sulfide having a weight average molecularweight in the range of about 50,000 g/mol to about 80,000 g/mol and acomplex viscosity in the range of about 200 Pa·s to about 900 Pa·s whenmeasured according to the Complex Viscosity Test defined herein; and (b)at least one tin additive comprising a branched tin(II) carboxylateselected from the group consisting of Sn(O₂CR)₂, Sn(O₂CR)(O₂CR′),Sn(O₂CR)(O₂CR″), and mixtures thereof, where the carboxylate moietiesO₂CR and O₂CR′ independently represent branched carboxylate anions andthe carboxylate moiety O₂CR″ represents a linear carboxylate anion.

This invention also relates to methods for decreasing the viscosity of apolyarylene sulfide melt while maintaining the molecular weight of thepolyarylene sulfide with time. Combining certain additives withpolyarylene sulfide has been found to decrease the complex viscosity ofthe composition by at least about 10% as compared to the complexviscosity of native polyarylene sulfide measured under the sameconditions.

DETAILED DESCRIPTION

This invention relates to methods for decreasing the complex viscosityof a polyarylene sulfide polymer melt while maintaining the molecularweight of the polyarylene sulfide with time. This invention also relatesto polymer melt compositions comprising a polyarylene sulfide and atleast one tin additive comprising a branched tin(II) carboxylate,wherein the complex viscosity of the composition is decreased relativeto the complex viscosity of a native polyarylene sulfide measured underthe same conditions, and the weight average molecular weight of thepolyarylene sulfide is maintained with time. The methods for decreasingthe complex viscosity of a polyarylene sulfide-containing polymer melt;and the polymer melt compositions so obtained, are useful in processesto produce fibers, films, coatings, nonwovens, and molded parts frompolyarylene sulfides.

Where the indefinite article “a” or “an” is used with respect to astatement or description of the presence of a step in a process of thisinvention, it is to be understood, unless the statement or descriptionexplicitly provides to the contrary, that the use of such indefinitearticle does not limit the presence of the step in the process to one innumber.

Where a range of numerical values is recited herein, unless otherwisestated, the range is intended to include the endpoints thereof, and allintegers and fractions within the range. It is not intended that thescope of the invention be limited to the specific values recited whendefining a range.

The following definitions are used herein and should be referred to forinterpretation of the claims and the specification.

The term “PAS” means polyarylene sulfide.

The term “PPS” means polyphenylene sulfide.

The term “native” refers to a polymer which does not contain anyadditives.

The term “secondary carbon atom” means a carbon atom that is bonded totwo other carbon atoms with single bonds.

The term “tertiary carbon atom” means a carbon atom that is bonded tothree other carbon atoms with single bonds.

The term “thermal stability”, as used herein, refers to the degree ofchange in the weight average molecular weight of a PAS polymer inducedby elevated temperatures in the absence of oxygen. As the thermalstability of a given PAS polymer improves, the degree to which thepolymer's weight average molecular weight changes over time decreases.Generally, in the absence of oxygen, changes in molecular weight areoften considered to be largely due to chain scission, which typicallydecreases the molecular weight of a PAS polymer.

The term “thermo-oxidative stability”, as used herein, refers to thedegree of change in the weight average molecular weight of a PAS polymerinduced by elevated temperatures in the presence of oxygen. As thethermo-oxidative stability of a given PAS polymer improves, the degreeto which the polymer's weight average molecular weight changes over timedecreases. Generally, in the presence of oxygen, changes in molecularweight may be due to a combination of oxidation of the polymer and chainscission. As oxidation of the polymer typically results incross-linking, which increases molecular weight, and chain scissiontypically decreases the molecular weight, changes in molecular weight ofa polymer at elevated temperatures in the presence of oxygen may bechallenging to interpret.

The term “° C.” means degrees Celsius.

The term “kg” means kilogram(s).

The term “g” means gram(s).

The term “mg” means milligram(s).

The term “mol” means mole(s).

The term “s” means second(s).

The term “min” means minute(s).

The term “hr” means hour(s).

The term “rpm” means revolutions per minute.

The term “rad” means radians.

The term “Pa” means pascals.

The term “psi” means pounds per square inch.

The term “mL” means milliliter(s).

The term “ft” means foot.

The term “weight percent” as used herein refers to the weight of aconstituent of a composition relative to the entire weight of thecomposition unless otherwise indicated. Weight percent is abbreviated as“wt %”.

Polyarylene sulfides (PAS) include linear, branched or cross linkedpolymers that include arylene sulfide units. Polyarylene sulfidepolymers and their synthesis are known in the art and such polymers arecommercially available.

Exemplary polyarylene sulfides useful in the invention includepolyarylene thioethers containing repeat units of the formula—[(Ar¹)_(n)—X]_(m)—[(Ar²)_(i)—Y]_(j)—(Ar³)_(k)—Z]_(l)—[(Ar⁴)_(o)—W]_(p)—wherein Ar¹, Ar², Ar³, and Ar⁴ are the same or different and are aryleneunits of 6 to 18 carbon atoms; W, X, Y, and Z are the same or differentand are bivalent linking groups selected from —SO₂—, —S—, —SO—, —CO—,—O—, —COO— or alkylene or alkylidene groups of 1 to 6 carbon atoms andwherein at least one of the linking groups is —S—; and n, m, i, j, k, l,o, and p are independently zero or 1, 2, 3, or 4, subject to the provisothat their sum total is not less than 2. The arylene units Ar¹, Ar²,Ar³, and Ar⁴ may be selectively substituted or unsubstituted.Advantageous arylene systems are phenylene, biphenylene, naphthylene,anthracene and phenanthrene. The polyarylene sulfide typically includesat least 30 mol %, particularly at least 50 mol % and more particularlyat least 70 mol % arylene sulfide (—S—) units. Preferably thepolyarylene sulfide polymer includes at least 85 mol % sulfide linkagesattached directly to two aromatic rings. Advantageously the polyarylenesulfide polymer is polyphenylene sulfide (PPS), defined herein ascontaining the phenylene sulfide structure —(C₆H₄—S)_(n)— (wherein n isan integer of 1 or more) as a component thereof.

A polyarylene sulfide polymer having one type of arylene group as a maincomponent can be preferably used. However, in view of processability andheat resistance, a copolymer containing two or more types of arylenegroups can also be used. A PPS resin comprising, as a main constituent,a p-phenylene sulfide recurring unit is particularly preferred since ithas excellent processability and is industrially easily obtained. Inaddition, a polyarylene ketone sulfide, polyarylene ketone ketonesulfide, polyarylene sulfide sulfone, and the like can also be used.

Specific examples of possible copolymers include a random or blockcopolymer having a p-phenylene sulfide recurring unit and an m-phenylenesulfide recurring unit, a random or block copolymer having a phenylenesulfide recurring unit and an arylene ketone sulfide recurring unit, arandom or block copolymer having a phenylene sulfide recurring unit andan arylene ketone ketone sulfide recurring unit, and a random or blockcopolymer having a phenylene sulfide recurring unit and an arylenesulfone sulfide recurring unit.

The polyarylene sulfides may optionally include other components notadversely affecting the desired properties thereof. Exemplary materialsthat could be used as additional components would include, withoutlimitation, antimicrobials, pigments, antioxidants, surfactants, waxes;flow promoters; particulates, and other materials added to enhanceprocessability of the polymer. These and other additives can be used inconventional amounts.

As noted above, PPS is an example of a polyarylene sulfide. PPS is anengineering thermoplastic polymer that is widely used for film, fiber,injection molding, and composite applications due to its high chemicalresistance, excellent mechanical properties, and good thermalproperties. However, the thermal and oxidative stability of PPS isconsiderably reduced in the presence of air and at elevated temperatureconditions. Under these conditions, severe degradation can occur,leading to the embitterment of PPS material and severe loss of strength.Improved thermal and oxidative stability of PPS at elevated temperaturesand in the presence of air are desired.

In one embodiment, the present invention provides methods for decreasingthe complex viscosity of a polyarylene sulfide polymer melt whilemaintaining the molecular weight of the polyarylene sulfide with time. Adecrease in the complex viscosity of a polyarylene sulfide polymer meltis desirable for a variety of reasons, including the ability to processthe melt at a lower temperature and with lower pressure drop duringfiber forming. Changes with time in the molecular weight of apolyarylene sulfide polymer heated in the presence of nitrogen are anindicator of the thermal stability of the polyarylene sulfide, withlarger changes in molecular weight indicating lower thermal stability.The extent to which a polymer melt can maintain the initial molecularweight of the polyarylene sulfide with time demonstrates the degree ofthermal stability of the polymer melt.

In one embodiment of the method, a polyarylene sulfide having a weightaverage molecular weight in the range of about 50,000 g/mol to about80,000 g/mol and a complex viscosity in the range of about 200 Pa·s toabout 900 Pa·s, when measured according to the Complex Viscosity Testdefined herein below, is combined with at least one additive asspecified herein below to form a polymer composition. The complexviscosity of the polymer composition is decreased compared to thecomplex viscosity of the native polyarylene sulfide measured under thesame conditions, and the retention of the weight average molecularweight of the polyarylene sulfide in the composition is at least about77% when measured according to the Accelerated Aging Test defined hereinbelow.

The term “measured under the same conditions”, as used herein, meansthat the complex viscosity of the polymer composition comprising theadditive and the complex viscosity of the native polyarylene sulfide aremeasured in accordance with ASTM D4440 at the same temperature and atthe same frequency and strain. The measurements may be made according tothe Complex Viscosity Test defined herein or at a temperature,frequency, and strain which are different from those of the ComplexViscosity Test.

The additive(s) and the polyarylene sulfide may be preblended as a drymixture before forming the polymer melt. Alternatively, the additive maybe compounded with the polyarylene sulfide in a masterbatch formulation,then diluted with additional polyarylene sulfide, as dry solids or asmelts. Generally, the additive is present in the polymer composition ata concentration of about 5 weight percent or less, based on the weightof the polyarylene sulfide. For example, the additive may be present inthe polymer composition at a concentration from about 0.1 weight percentto about 5 weight percent, of from about 0.1 weight percent to about 4weight percent, or from about 0.1 weight percent to about 3 weightpercent, or from about 0.1 weight percent to about 2 weight percent, orfrom about 0.1 to about 1 weight percent. Typically, the concentrationof the additive may be higher in a master batch composition, for examplefrom about 5 weight percent to about 10 weight percent, or higher. Theadditive may be added to the molten or solid polyarylene sulfide as asolid, as a slurry, or as a solution.

In one embodiment, the at least one additive is selected from the groupconsisting of tin(IV) oxide, tin(II) oxide, tin(II) stearate, zincstearate, zinc acetate, zinc oxide, a branched tin(II) carboxylate; andmixtures thereof. The additives may be obtained commercially. The choiceof additive may depend on the desired polymer viscosity decrease.

In one embodiment, a polyarylene sulfide is combined with an additivecomprising zinc acetate, whereby the complex viscosity of thecomposition is decreased by about 10% to about 20% relative to thecomplex viscosity of the native polyarylene sulfide measured under thesame conditions.

In one embodiment, a polyarylene sulfide is combined with an additivecomprising zinc stearate, whereby the complex viscosity of thecomposition is decreased by about 20% to about 30% relative to thecomplex viscosity of the native polyarylene sulfide measured under thesame conditions.

In one embodiment, a polyarylene sulfide is combined with an additivecomprising tin(II) stearate, whereby the complex viscosity of thecomposition is decreased by at least about 40% relative to the complexviscosity of the native polyarylene sulfide measured under the sameconditions.

In one embodiment, the additive may comprise at least one tin additivecomprising a branched tin(II) carboxylate selected from the groupconsisting of Sn(O₂CR)₂, Sn(O₂CR)(O₂CR′), Sn(O₂CR)(O₂CR″), and mixturesthereof, were the carboxylate moieties O₂CR and O₂CR′ independentlyrepresent branched carboxylate anions and the carboxylate moiety O₂CR″represents a linear carboxylate anion. In one embodiment, the branchedtin(II) carboxylate comprises Sn(O₂CR)₂, Sn(O₂CR)(O₂CR′), or a mixturethereof. In one embodiment, the branched tin(II) carboxylate comprisesSn(O₂CR)₂. In one embodiment, the branched tin(II) carboxylate comprisesSn(O₂CR)(O₂CR′). In one embodiment, the branched tin(II) carboxylatecomprises Sn(O₂CR)(O₂CR″).

Optionally, the tin additive may further comprise a linear tin(II)carboxylate Sn(O₂CR″)₂. Generally, the relative amounts of the branchedand linear tin(II) carboxylates are selected such that the sum of thebranched carboxylate moieties [O₂CR+O₂CR′] is at least about 25% on amolar basis of the total carboxylate moieties [O₂CR+O₂CR′+O₂CR″]contained in the additive. For example, the sum of the branchedcarboxylate moieties may be at least about 33%, or at least about 40%,or at least about 50%, or at least about 66%, or at least about 75%, orat least about 90%, of the total carboxylate moieties contained in thetin additive.

In one embodiment, the radicals R and R both comprise from 6 to 30carbon atoms and both contain at least one secondary or tertiary carbon.The secondary or tertiary carbon(s) may be located at any position(s) inthe carboxylate moieties O₂CR and O₂CR′, for example in the position αto the carboxylate carbon, in the position ω to the carboxylate carbon,and at any intermediate position(s). The radicals R and R′ may beunsubstituted or may be optionally substituted with inert groups, forexample with fluoride, chloride, bromide, iodide, nitro, hydroxyl, andcarboxylate groups. Examples of suitable organic R and R″ groups includealiphatic, aromatic, cycloaliphatic, oxygen-containing heterocyclic,nitrogen-containing heterocyclic, and sulfur-containing heterocyclicradicals. The heterocyclic radicals may contain carbon and oxygen,nitrogen, or sulfur in the ring structure.

In one embodiment, the radical R″ is a primary alkyl group comprisingfrom 6 to 30 carbon atoms, optionally substituted with inert groups, forexample with fluoride, chloride, bromide, iodide, nitro, hydroxyl, andcarboxylate groups. In one embodiment, the radical R″ is a primary alkylgroup comprising from 6 to 20 carbon atoms.

In one embodiment, the radicals R or R″ independently or both have astructure represented by Formula (I),

wherein R₁, R₂, and R₃ are independently:

H:

a primary, secondary, or tertiary alkyl group having from 6 to 18 carbonatoms, optionally substituted with fluoride, chloride, bromide, iodide,nitro, hydroxyl, and carboxyl groups;

an aromatic group having from 6 to 18 carbon atoms, optionallysubstituted with alkyl, fluoride, chloride, bromide, iodide, nitro,hydroxyl, and carboxyl groups; and

a cycloaliphatic group having from 6 to 18 carbon atoms, optionallysubstituted with fluoride, chloride, bromide, iodide, nitro, hydroxyl,and carboxyl groups:

with the proviso that when R₂ and R₃ are H, R₁ is:

a secondary or tertiary alkyl group having from 6 to 18 carbon atoms,optionally substituted with fluoride, chloride, bromide, iodide, nitro,hydroxyl, and carboxyl groups;

an aromatic group having from 6 to 18 carbons atoms and substituted witha secondary or tertiary alkyl group having from 6 to 18 carbon atoms,the aromatic group and/or the secondary or tertiary alkyl group beingoptionally substituted with fluoride, chloride, bromide, iodide, nitro,hydroxyl, and carboxyl groups; and

a cycloaliphatic group having from 6 to 18 carbon atoms, optionallysubstituted with fluoride, chloride, bromide, iodide, nitro, hydroxyl,and carboxyl groups.

In one embodiment, the radicals R or R′ or both have a structurerepresented by Formula (I), and R₃ is H.

In another embodiment, the radicals R or R′ or both have a structurerepresented by Formula (II),

wherein

R₄ is a primary, secondary, or tertiary alkyl group having from 4 to 6carbon atoms, optionally substituted with fluoride, chloride, bromide,iodide, nitro, and hydroxyl groups; and

R₅ is a methyl, ethyl, n-propyl, sec-propyl, n-butyl, sec-butyl, ortert-butyl group, optionally substituted with fluoride, chloride,bromide, iodide, nitro, and hydroxyl groups.

In one embodiment, the radicals R and R′ are the same and both have astructure represented by Formula (II), where R₄ is n-butyl and R₅ isethyl. This embodiment describes the branched tin(II) carboxylatetin(II) 2-ethylhexanoate, also referred to herein as tin(II)ethylhexanoate.

The tin(II) carboxylate(s) may be obtained commercially, or may begenerated in situ from an appropriate source of tin(H) cations and thecarboxylic acid corresponding to the desired carboxylate(s).

In one embodiment, the polyarylene sulfide composition comprising thebranched tin(II) carboxylate further comprises at least one zinc(II)compound and/or zinc metal [Zn(0)]. The zinc(II) compound may be anorganic compound, for example zinc stearate, or an inorganic compoundsuch as zinc sulfate or zinc oxide, as long as the organic or inorganiccounter ions do not adversely affect the desired properties of thepolyarylene sulfide composition. The zinc(II) compound may be obtainedcommercially, or may be generated in situ. Zinc metal may be used in thecomposition as a source of zinc(II) ions, alone or in conjunction withat least one zinc(II) compound. In one embodiment the zinc(II) compoundis selected from the group consisting of zinc oxide, zinc stearate, andmixtures thereof.

The zinc(II) compound and/or zinc metal may be present in thepolyarylene sulfide at a concentration of about 10 weight percent orless, based on the weight of the polyarylene sulfide. For example, thezinc(II) compound and/or zinc metal may be present at a concentration ofabout 0.01 weight percent to about 5 weight percent, or for example fromabout 0.25 weight percent to about 2 weight percent. Typically, theconcentration of the zinc(II) compound and/or zinc metal may be higherin a master batch composition, for example from about 5 weight percentto about 10 weight percent, or higher. The at least one zinc(II)compound and/or zinc metal may be added to the molten or solidpolyarylene sulfide as a solid, as a slurry, or as a solution. Thezinc(II) compound and/or zinc metal may be added together with thetin(II) additive or separately.

In another embodiment, the present invention provides polymer meltcompositions comprising a polyarylene sulfide having a weight averagemolecular weight in the range of about 50,000 gμmol to about 80,000g/mol and a complex viscosity in the range of about 200 Pa·s to about900 Pas when measured according to the Complex Viscosity Test definedherein, and at least one tin additive comprising a branched tin(II)carboxylate selected from the group consisting of Sn(O₂CR)₂,Sn(O₂CR)(O₂CR′), Sn(O₂CR)(O₂CR″), and mixtures thereof, where thecarboxylate moieties O₂CR and O₂CR′ independently represent branchedcarboxylate anions and the carboxylate moiety O₂CR″ represents a linearcarboxylate anion. The complex viscosity of the polymer composition isdecreased compared to the complex viscosity of the native polyarylenesulfide measured under the same conditions, and the retention of theweight average molecular weight of the polyarylene sulfide in thecomposition is at least about 80% when measured according to theAccelerated Aging Test defined herein below. The definitions of R, R′,and R″ are as defined above.

In one embodiment, the additive further comprises a linear tin(II)carboxylate Sn(O₂CR″)₂ and R″ is as defined above. In one embodiment,the tin(II) carboxylate comprises Sn(O₂CR)₂, Sn(O₂CR)(O₂CR′), ormixtures thereof, and the radicals R or R are as defined above. In oneembodiment, the tin(II) carboxylate comprises Sn(O₂CR)₂, and R has astructure represented by Formula (II), where R₄ is n-butyl and R₅ isethyl.

In one embodiment, the complex viscosity of the polymer composition isdecreased by at least about 30% relative to the complex viscosity of thenative polyarylene sulfide measured under the same conditions. In oneembodiment, the polymer composition further comprises at least onezinc(II) compound and/or zinc metal. In one embodiment, the zinc(II)compound comprises zinc stearate, the additive comprises Sn(O₂CR)₂, andR has a structure represented by Formula (II), where R₄ is n-butyl andR₅ is ethyl. In one embodiment, the polyarylene sulfide is polyphenylenesulfide.

Generally, the additive is present in the polymer melt composition at aconcentration of about 5 weight percent or less, based on the weight ofthe polyarylene sulfide. For example, the additive may be present in thepolymer melt composition at a concentration from about 0.1 weightpercent to about 5 weight percent, of from about 0.1 weight percent toabout 4 weight percent, or from about 0.1 weight percent to about 3weight percent, or from about 0.1 weight percent to about 2 weightpercent, or from about 0.1 to about 1 weight percent. Typically, theconcentration of the additive may be higher in a master batchcomposition, for example from about 5 weight percent to about 10 weightpercent, or higher. The additive may be added to the molten or solidpolyarylene sulfide as a solid, as a slurry, or as a solution.

EXAMPLES

The present invention is further defined in the following examples. Itshould be understood that these examples, while indicating preferredembodiments of the invention, are given by way of illustration only.From the above discussion and these examples, one skilled in the art canascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various uses andconditions.

Materials

The following materials were used in the examples. All commercialmaterials were used as received unless otherwise indicated. Fortron® 309polyphenylene sulfide and Fortron® 317 polyphenylene sulfide wereobtained from Ticona (Florence, Ky.). Tin(II) 2-ethylhexanoate (90%),zinc acetate dihydrate (98%), calcium acetate dehydrate (98%) and zincoxide (99%) were obtained from Sigma-Aldrich (St. Louis, Mo.). Tin(II)stearate (98%) was obtained from Acros Organics (Morris Plains, N.J.).Zinc stearate (99%) was obtained from Honeywell Reidel-de Haen (Seelze,Germany). Tin(IV)oxide (99.9%), tin(II)oxide (98%) and calcium stearate(85%) were obtained from Strem Chemicals (Newburyport, Mass.). Calciumcarbonate was obtained from VWR International (West Chester Pa.).

Tin(II) 2-ethylhexanoate is also referred to herein as tin(II)ethylhexanoate.

For each Example and Comparative Example, different samples of thecomposition to be evaluated were used for complex viscosity and formolecular weight measurements.

Analytical Methods

Complex viscosity was measured at 300° C. under nitrogen in accordancewith ASTM D 4440 using a Malvern controlled-stress rotational rheometerequipped with an extended temperature cell (ETC) forced convection ovenand 25 mm parallel plates with smooth surfaces. Plate temperature wascalibrated using a disc made of nylon with a thermocouple embedded inthe middle. Disks with a diameter of 25 mm and a thickness of 1.2 mmwere prepared from pellets of the compositions of the Examples and theComparative Examples by compression molding under vacuum at atemperature of 290° C. using a Dake heated laboratory press.

To perform complex viscosity measurements, a molded disk of the PPScomposition was inserted between the parallel plates preheated to 300°C., the door of the forced convection oven was closed, the gap waschanged to around 3200 irn to prevent curling of the disk, and the oventemperature was allowed to re-equilibrate to 300° C. The gap was thenchanged from 3200 to 1050 μm, the oven was opened, the edges of thesample were carefully trimmed, the oven was closed, the oven temperaturewas allowed to re-equilibrate to 300° C., the gap was adjusted to 1000μm, and the measurement started. A time sweep was performed at afrequency of 6.283 rad/s using a strain of 10%. The measurement wasperformed in duplicate with a fresh sample loading each time and theaverage values are reported in Table 1. This method is referred toherein as the “Complex Viscosity Test”.

The change in viscosity was calculated as follows and expressed as apercentage:

Visc change(%)=[(Viso(control)−Visc (comp))/Visc (control)]×100

were Visc (control) is the viscosity of the native polyarylene sulfidemeasured at 180 s after the start of the test and Visc (comp) is theviscosity of the polyarylene sulfide composition containing the additivemeasured at 180 s after the start of the test. Visc (control) and Visc(comp) are measured under the same conditions.

The thermal stability of PPS compositions was assessed by measuringchanges in molecular weight (MW) under nitrogen as a function of timeusing the method described herein, which is referred to as the“Accelerated Aging Test”. To assess changes in molecular weight, sampleswere heat-treated in nitrogen and compared with untreated samples. Toheat-treat a sample, a 12″ aluminum block containing 17×28 mm holes waspreheated in a nitrogen-purged dry box to 320° C. using an IKA hotplate.Pellets (0.5 g) of the compositions of the Examples and the ComparativeExamples were placed in 40 mL vials (26 mm×95 mm) and inserted into thepreheated block for 2 h, removed, and allowed to cool to roomtemperature. The resulting monolithic mass of heat-treated polymer wassubsequently removed from each vial by immersion in liquid nitrogenfollowed by breaking the vial with a hammer after removal from theliquid nitrogen.

The molecular weights of the heat-treated and non-heat-treated sampleswere measured using an integrated multidetector SEC system PL-220™ fromPolymer Laboratories Ltd., now a part of Varian Inc. (Church Stretton,UK). Constant temperature was maintained across the entire path of apolymer solution from the injector through the four on-linedetectors: 1) a two-angle light scattering photometer, 2) a differentialrefractometer, 3) a differential capillary viscometer, and 4) anevaporative light scattering photometer (ELSD). The system was run withclosed valves for the ELSD detector, so that only traces from therefractometer, viscometer and light scattering photometer werecollected. Three chromatographic columns were used: two Mix-B PL-Gelcolumns and one 500A PL Gel column from Polymer Labs (10 μm particlesize). The mobile phase was comprised of 1-chloronaphthalene (1-CNP)(Acros Organics), which was filtered through a 0.2 micron PTFE membranefilter prior to use. The oven temperature was set to 210° C.

Typically, a PPS sample was dissolved for 2 hours in 1-CNP at 250° C.with continuous moderate agitation without filtration (Automatic samplepreparation system PL 260™ from Polymer Laboratories). Subsequently, thehot sample solution was transferred into a hot (220° C.) 4 mL injectionvalve at which point it was immediately injected and eluted in thesystem. The following set of chromatographic conditions was employed:1-CNP temperature: 220° C. at injector, 210° C. at columns anddetectors; flow rate: 1 mL/min, sample concentration: 3 mg/mL, injectionvolume: 0.2 mL, run time: 40 min. Molecular weight distribution (MWD)and average molecular weights of PPS were then calculated using amultidetector SEC method implemented in Empower™ 2.0 Chromatography DataManager from Waters Corp. (Milford, Mass.).

Molecular weight retention was calculated as follows and expressed as apercentage:

Mw Retention(%)=[1−[(Mw(initial)−Mw(final))/Mw(initial)]]×100

where Mw (initial) is the molecular weight of the composition at thestart of the thermal stability test and Mw (final) is the molecularweight of the composition after aging for 2 hours at 320° C. innitrogen.

In the Table, “Ex” means “Example” and “Comp Ex” means “ComparativeExample”. A negative value for “Change in Complex Viscosity (%)”indicates that the complex viscosity of the sample is decreased relativeto that for native PPS (Comparative Example A). A positive value for“Change in Complex Viscosity (%)” indicates that the complex viscosityof the sample is increased relative to that for native PPS (ComparativeExample A).

Values are reported as average value uncertainty. Following standardconvention, the uncertainty was rounded to 1 significant figure and theaverage value was rounded to the same number of decimal places as theuncertainty. The average values reported in the Table are the meanobtained from a minimum of two runs and the uncertainty is the standarderror of the mean. For the weight average molecular weight theuncertainty is 1000 g/mol and for the complex viscosity the uncertaintyis 10 Pa·s.

Example 1 PPS Containing Tin(II) Ethylhexanoate

This Example shows the results for tin(II) ethylhexanoate as an additivein polyphenylene sulfide. A PPS composition containing 0.58 weightpercent (0.014 mol/Kg) tin(II) ethylhexanoate was prepared as follows.Fortron® 309 PPS (700 g), Fortran® 317 PPS (300 g), and tin(II)ethylhexanoate (6.48 g) were combined in a glass jar, manually mixed,and placed on a Stoneware bottle roller for 5 min. The resultant mixturewas subsequently melt compounded using a Coperion 18 mm intermeshingco-rotating twin-screw extruder. The conditions of extrusion included amaximum barrel temperature of 300° C., a maximum melt temperature of310° C., screw speed of 300 rpm, with a residence time of approximately1 minute and a die pressure of 14-15 psi at a single strand die. Thestrand was frozen in a 6 ft tap water trough prior to being pelletizedby a Conair chopper to give a pellet count of 100-120 pellets per gram.896 g of the pelletized composition was obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 2 PPS Containing Tin(II) Ethylhexanoate and Zinc Oxide

This Example shows the results for tin(II) ethylhexanoate and zinc oxideas additives in polyphenylene sulfide. A PPS composition containing 0.58weight percent (0.014 mol/Kg) tin(II) ethylhexanoate and 0.13 weightpercent (0.016 mol/Kg) zinc oxide was prepared as described in Example1, except that 6.48 grams of tin(II) ethylhexanoate and 1.30 grams ofzinc oxide were combined with 700 g Fortron® 309 PPS and 300 g Fortron®317 PPS. 866 Grams of the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 3 PPS Containing Tin(II) Ethylhexanoate and Zinc Stearate

This Example shows the results for tin(II) ethylhexanoate and zincstearate as additives in polyphenylene sulfide. A PPS compositioncontaining 0.58 weight percent (0.014 mol/Kg) tin(II) ethylhexanoate and1.0 weight percent (0.016 mol/Kg) zinc stearate was prepared asdescribed in Example 1, except that 6.48 grams of tin(II) ethylhexanoateand 10.12 grams of zinc stearate were combined with 700 g of Fortron®309 PPS and 300 g of Fortron® 317 PPS, 873 Grams of the pelletizedcomposition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 4 PPS Containing Tin(IV) Oxide and Tin(II) Stearate

This Example shows the results for tin(IV) oxide and tin(II) stearate asadditives in polyphenylene sulfide. A PPS composition containing 0.24weight percent (0.016 mol/kg) tin(IV) oxide and 1.1 weight percent 0.016mol/kg) tin stearate was prepared as described in Example 1, except that2.41 grams of tin(IV) oxide and 10.97 grams of tin(II) stearate werecombined with 700 g of Fortron® 309 PPS and 300 g of Fortron® 317 PPS.893 Grams of the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 5 PPS Containing Tin(II) Stearate

This Example shows the results for tin(II) stearate as an additive inpolyphenylene sulfide. A PPS composition containing 1.1 weight percent(0.016 mol/Kg) tin stearate was prepared as described in Example 1,except that 10.97 grams of tin(II) stearate were combined with 700 g ofFortron® 309 PPS and 300 g of Fortron® 317 PPS. 797 Grams of thepelletized composition were yielded.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 6 PPS Containing Zinc Stearate

This Example shows the results for zinc stearate as an additive inpolyphenylene sulfide. A PPS composition containing 1.0 weight percent(0.016 mol/Kg) zinc stearate was prepared as described in Example 1,except that 10.12 grams of zinc stearate were combined with 700 g ofFortron® 309 PPS and 300 g of Fortron® 317 PPS. 784 grams of thepelletized composition were yielded.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 7 PPS Containing Zinc Stearate and Tin(II) Oxide

This Example shows the results for zinc stearate and tin(II) oxide asadditives in polyphenylene sulfide. A PPS composition containing 1.0weight percent (0.016 mol/kg) zinc stearate and 0.22 weight percent(0.016 mol/Kg) tin(II) oxide was prepared as described in Example 1,except that 10.12 grams of zinc stearate and 2.16 grams of tin(II) oxidewere combined with 700 g of Fortron® 309 PPS and 300 g of Fortron® 317PPS. 860 grams of the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 8 PPS Containing Zinc Stearate and Zinc Oxide

This Example shows the results for zinc stearate and zinc oxide asadditives in polyphenylene sulfide. A PPS composition containing 1.0weight percent (0.016 mol/Kg) zinc stearate and 0.13 weight percent(0.016 mol/Kg) zinc oxide was prepared as described in Example 1, exceptthat 10.12 grams of zinc stearate and 1.30 grams of zinc oxide werecombined with 700 g of Fortron® 309 PPS and 300 g of Fortron® 317 PPS.858 grams of the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 9 PPS Containing Zinc Acetate

This Example shows the results for zinc acetate as an additive inpolyphenylene sulfide. A PPS composition containing 0.35 weight percent(0.016 mol/kg) zinc acetate dihydrate was prepared as described inExample 1, except that 3.51 grams of zinc acetate dihydrate werecombined with 700 g of Fortron® 309 PPS and 300 g of Fortron® 317 PPS.801 grams of the pelletized composition were obtained,

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Example 10 PPS Containing Tin(II) Stearate and Zinc Stearate

This Example shows the results for tin(II) stearate and zinc stearate asco-additives in polyphenylene sulfide. A PPS composition containing 1.0weight percent (0.016 mol/kg) zinc stearate and 1.1 weight percent(0.016 mol/kg) tin(II) stearate was prepared as described in Example 1,except that 10.12 grams of zinc stearate and 10.97 grams of tin stearatewere combined with 700 g of Fortron® 309 PPS and 300 g of Fortron® 317PPS. 857 Grams of the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Comparative Example A PPS Control (No Additives)

This Comparative Example is a control showing the results ofpolyphenylene sulfide without an additive, which is referred to asnative PPS. A PPS composition was prepared as described in Example 1using 700 g Fortron® 309 PPS and 300 g Fortron® 317 PPS but no othercompounds were added. 829 Grams of the pelletized composition wereobtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Comparative Example B PPS Containing Calcium Carbonate

This Comparative Example shows the results for calcium carbonate as anadditive in polyphenylene sulfide. A PPS composition containing 0.16weight percent (0.016 mol/kg) calcium carbonate was prepared asdescribed in Example 1, except that 1.6 grams of calcium carbonate werecombined with 700 g of Fortron® 309 PPS and 300 g of Fortron® 317 PPS.743 grams of the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Comparative Example C PPS Containing Calcium Stearate

This Comparative Example shows the results for calcium stearate as anadditive in polyphenylene sulfide. A PPS composition containing 0.97weight percent (0.016 mol/Kg) calcium stearate was prepared as describedin Example 1, except that 9.71 grams of calcium stearate were combinedwith 700 g of Fortran® 309 PPS and 300 g of Fortran®, 317 PPS. 815 gramsof the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

Comparative Example D PPS Containing Calcium Acetate

This Comparative Example shows the results for calcium acetate as anadditive in polyphenylene sulfide. A PPS composition containing 0.25weight percent (0.016 mol/Kg) calcium acetate dihydrate was prepared asdescribed in Example 1, except that 2.53 grams of calcium acetatedihydrate were combined with 700 g of Fortron® 309 PPS and 300 g ofFortron® 317 PPS. 806 grams of the pelletized composition were obtained.

The viscosity and molecular weight of the pelletized composition weredetermined in the melt using the analytical techniques described above.Results are presented in Table 1.

TABLE 1 Complex Viscosity MW after 2 hours at 180 s Change in of agingInitial in Complex at 320° C. in MW MW nitrogen Viscosity nitrogenRetention Sample Additive(s) (g/mol) (Pa · s) (%) (g/mol) (%) Ex 1 tin57,000 120 −52 49,000 86 ethylhexanoate Ex 2 tin 59,000 140 −44 51,00086 ethylhexanoate + zinc oxide Ex 3 tin 58,000 120 −52 54,000 93ethylhexanoate + zinc stearate Ex 4 tin(IV) oxide + 56,000 150 −4050,000 89 tin stearate Ex 5 tin stearate 60,000 110 −56 46,000 77 Ex 6zinc stearate 60,000 190 −24 57,000 95 Ex 7 zinc stearate + 60,000 180−28 59,000 98 tin(II) oxide Ex 8 zinc stearate + 60,000 200 −20 57,00095 zinc oxide Ex 9 zinc acetate 60,000 210 −16 55,000 92 Ex 10 tinstearate + 60,000 120 −52 52,000 87 zinc stearate Comp Ex A — 60,000 2500 46,000 77 Comp Ex B calcium 61,000 280 12 45,000 74 carbonate Comp ExC calcium 60,000 270 8 49,000 82 stearate Comp Ex D calcium acetate58,000 270 8 49,000 84

The Examples show a decrease in viscosity relative to the nativepolyphenylene sulfide while maintaining at least 77% retention of themolecular weight after aging for 2 hours at 320 in nitrogen. Examples 1,2, and 3 with tin(II) ethylhexanoate show a decrease in viscosityrelative to the native polyphenylene sulfide while maintaining at least85% retention of the molecular weight after aging for 2 hours at 320° C.in nitrogen. Comparative Examples B, C, and D show an increase inviscosity relative to the native polyphenylene sulfide while maintainingat least a 74% retention of the molecular weight after aging for 2 hoursat 320° C. in nitrogen. Comparative Example A, containing native PPS(without any additives), shows a 77% retention of molecular weight afteraging for 2 hours at 320° C. in nitrogen.

Although particular embodiments of the present invention have beendescribed in the foregoing description, it will be understood by thoseskilled in the art that the invention is capable of numerousmodifications, substitutions, and rearrangements without departing fromthe spirit of essential attributes of the invention. Reference should bemade to the appended claims, rather than to the foregoing specification,as indicating the scope of the invention.

1. A polymer melt composition comprising: (a) a polyarylene sulfidehaving a weight average molecular weight in the range of about 50,000g/mol to about 80,000 g/mol and a complex viscosity in the range ofabout 200 Pa·s to about 900 Pa·s when measured according to the ComplexViscosity Test defined herein; and (b) at least one tin additivecomprising a branched tin(II) carboxylate selected from the groupconsisting of Sn(O₂CR)₂, Sn(O₂CR)(O₂CR′), Sn(O₂CR)(O₂CR″), and mixturesthereof, where the carboxylate moieties O₂CR and O₂CR independentlyrepresent branched carboxylate anions and the carboxylate moiety O₂CR″represents a linear carboxylate anion.
 2. The composition of claim 1,wherein the additive further comprises a linear tin(II) carboxylateSn(O₂CR″)₂, where R″ is a primary alkyl group comprising from 6 to 30carbon atoms.
 3. The composition of claim 1, wherein the tin(II)carboxylate comprises Sn(O₂CR)₂, Sn(O₂CR)(O₂CR), or mixtures thereof,and the radicals R or R′ independently or both have a structurerepresented by Formula (I),

wherein R₁, R₂, and R₃ are independently: H; a primary, secondary, ortertiary alkyl group having from 6 to 18 carbon atoms, optionallysubstituted with fluoride, chloride, bromide, iodide, nitro, hydroxyl,and carboxyl groups; an aromatic group having from 6 to 18 carbon atoms,optionally substituted with alkyl, fluoride, chloride, bromide, iodide,nitro, hydroxyl, and carboxyl groups; and a cycloaliphatic group havingfrom 6 to 18 carbon atoms, optionally substituted with fluoride,chloride, bromide, iodide, nitro, hydroxyl, and carboxyl groups; withthe proviso that when R₂ and R₃ are H, R₁ is: a secondary or tertiaryalkyl group having from 6 to 18 carbon atoms, optionally substitutedwith fluoride, chloride, bromide, iodide, nitro, hydroxyl, and carboxylgroups; an aromatic group having from 6 to 18 carbons atoms andsubstituted with a secondary or tertiary alkyl group having from 6 to 18carbon atoms, the aromatic group and/or the secondary or tertiary alkylgroup being optionally substituted with fluoride, chloride, bromide,iodide, nitro, hydroxyl, and carboxyl groups; and a cycloaliphatic grouphaving from 6 to 18 carbon atoms, optionally substituted with fluoride,chloride, bromide, iodide, nitro, hydroxyl, and carboxyl groups.
 4. Thecomposition of claim 3, wherein the radicals R or R′ or both have astructure represented by Formula (I), and R₃ is H.
 5. The composition ofclaim 1, wherein the tin(H) carboxylate comprises Sn(O₂CR)₂,Sn(O₂CR)(O₂CR′), or mixtures thereof, and the radicals R or R′ or bothhave a structure represented by Formula (H),

wherein R₁ is a primary, secondary, or tertiary alkyl group having from4 to 6 carbon atoms, optionally substituted with fluoride, chloride,bromide, iodide, nitro, and hydroxyl groups; and R₅ is a methyl, ethyl,n-propyl, sec-propyl, n-butyl, sec-butyl, or tert-butyl group,optionally substituted with fluoride, chloride, bromide, iodide, nitro,and hydroxyl groups.
 6. The composition of claim 5, wherein the tin(II)carboxylate comprises Sn(O₂CR)₂, and R has a structure represented byFormula (II), where R₄ is n-butyl and R₅ is ethyl.
 7. The composition ofclaim 1, wherein the complex viscosity of the polymer composition isdecreased by at least about 30% relative to the complex viscosity of thenative polyarylene sulfide measured under the same conditions.
 8. Thecomposition of claim 1, further comprising at least one zinc(II)compound and/or zinc metal.
 9. The composition of claim 8, wherein thezinc(II) compound comprises zinc stearate, the additive comprisesSn(O₂CR)₂, and R has a structure represented by Formula (II)

where R₄ is n-butyl and R₅ is ethyl.
 10. The composition of claim 1,wherein the additive is present in the polymer composition at aconcentration of about 5 weight percent or less, based on the weight ofthe polyarylene sulfide.
 11. The composition of claim 1, wherein thepolyarylene sulfide is polyphenylene sulfide.
 12. The composition ofclaim 1, wherein the complex viscosity of the melt composition isdecreased compared to that of the native polyarylene sulfide measuredunder the same conditions; and/or the retention of the weight averagemolecular weight of the polyarylene sulfide in the composition is atleast about 80% when measured according to the Accelerated Aging Testdefined herein.